The conduits in such heat exchangers may be of many shapes but in certain applications, such as for dry-type cooling towers, they may conveniently be panels formed from two layers of sheet material, bends in the sheets forming the cavities in which the first fluid is accommodated. With this type of construction the surfaces of the conduits, except where seams exist separating adjacent conduits in the panel, can be generally planar, although it is often advantageous to introduce local corrugations in the conduit surfaces, extending at right angles to the direction of flow in the conduits, in order to extend the surface area exposed to the fluids, to induce turbulent fluid flow, and to provide seating formations for the fins. In such cases the fins may suitably be strips of metal from which portions are removed or pressed out of their original planes. Heat exchangers of this type can be highly efficient and it is possible to manufacture them economically. They are however expensive to assemble because of the laborious task of inserting the numerous fin strips in place between the conduit panels. Moreover, since the direction of the flow of the fluid traversing the fins is necessarily at right angles to the direction of flow of the fluid in the conduits (i.e. a cross-flow arrangement), the inherent capability of the heat exchanger is somewhat removed from the ideal.
The ideal situation is a counter-flow arrangement, in which the directions of flow of the two fluids are opposite to each other.
It is an object of the invention to provide a heat exchanger having adequate provision for the extension of the conduit surfaces, but in which some of the disadvantages of known heat exchangers, particularly those of the type mentioned above, are mitigated or overcome.